The present invention relates to fluid spray guns, and more particularly to fluid spray guns utilizing compressed air through selectively placed passages to properly atomize and shape the atomized fluid discharged from the spray gun. The invention specifically relates to a method for precisely fixing an annular air passage about an axially disposed fluid orifice, and the apparatus resulting therefrom.
Paint spray guns utilizing compressed air as an aid in the atomization and control of the spray pattern are well known in the prior art. Such spray guns utilize critically placed air passages to direct air at the fluid jet emitted from the front of the spray gun, to break up the jet into very fine droplets, and also to form the droplets into an acceptable pattern for spraying. These air passages are utilized to form a generally elliptically shaped spray pattern, which has gained acceptance in the painting industry as enabling a uniform distribution of paint on an article to be coated. The number and type of such air passages has been varied, depending upon individual spray gun designs and manufacturer preferences, although certain similarities are usually found in air spray guns regardless of the manufacturer. For example, it has become generally accepted by the industry to provide forwardly projecting horns in front of the fluid orifice, with the horns having one or more air passages for directing air flow toward the atomized paint particles, thereby serving to shape the particles into the desired spray pattern. Further, a great many manufacturers utilize an annular air passage axially surrounding the fluid orifice to provide a source of compressed air for initially atomizing the paint in the fluid orifice as it is emitted from the orifice. Still further, many manufacturers provide additional passages more or less diametrically opposed about the fluid orifice to provide additional atomization and shaping air for the paint spray pattern.
Of all of the air passages associated with an air spray gun, perhaps the most critical passage is the annular spray passage which typically surrounds the fluid orifice. In the usual construction, the fluid orifice projects through the front of the spray nozzle by a short distance, and is surrounded by an annular air gap which passes pressurized air. The air must be equally distributed about this annular air gap in order that the fluid stream can be evenly atomized and some form of spray pattern control can be maintained. The coaxial alignment of this annular air gap with the fluid orifice is extremely critical, because even extremely small amounts of coaxial misalignment result in significant unbalances in the delivery of pressurized air about the air gap, causing the atomized spray pattern to deflect off-axis by significant amounts. If the spray pattern is deflected off-axis, the air passages associated with shaping the spray pattern into desired form produce spray pattern distortion, with the result that the spray gun is essentially nonfunctional for its intended purpose. Therefore, a great amount of attention has been devoted to the problem of coaxially aligning the fluid orifice and the annular spray gap around the orifice. For example, U.S. Pat. No. 2,715,046, issued Aug. 9, 1955 discloses a spray nozzle having an adjustable aperture for properly coaxially positioning the fluid spray orifice with respect to the annular air gap. Yet another approach is disclosed in U.S. Pat. No. 4,273,293, issued June 16, 1981, wherein the fluid orifice is retained in coaxial position by radially extending ribs and a plurality of circumferentially spaced passages between the ribs. In this patent, the coaxial annular air gap is sacrificed to some extent in order that the fluid orifice may be properly centered with respect to a plurality of individual circumferentially aligned air passages. Of necessity, these individual air passages must be constructed of quite small size, and are therefore subject to clogging to a greater extent than a larger air passage might be subjected.
It is therefore desirable to provide a spray gun having a precisely located annular air gap about a fluid orifice in coaxial arrangement, wherein air is evenly distributed about the fluid orifice. Further it is desirable to construct an air cap having such characteristics according to as simple and economical a process as possible.